oop_exercises.py

# ==========================================
# Python Learning Lab: 05 OOP
# ==========================================

print("--- Running OOP Exercises ---")

# ==========================================
# Challenge 1: Basic Class & Encapsulation
# ==========================================
# Implement a `BankAccount` class with:
# - A private attribute `__balance` initialized to a given amount.
# - A property getter `balance` to view the balance.
# - A method `deposit(amount)` that increases balance.
# - A method `withdraw(amount)` that decreases balance if sufficient funds exist,
#   otherwise raises a ValueError.

class BankAccount:
    def __init__(self, initial_balance):
        # TODO: Initialize private balance variable
        self.__balance = initial_balance

    @property
    def balance(self):
        # TODO: Return private balance
        return self.__balance

    def deposit(self, amount):
        # TODO: Increase private balance
        self.__balance += amount

    def withdraw(self, amount):
        # TODO: Decrease balance or raise ValueError
        if amount > self.__balance:
            raise ValueError("Insufficient funds")
        self.__balance -= amount

# --- Verification ---
account = BankAccount(100)
assert account.balance == 100, "Getter failed to retrieve correct balance"
account.deposit(50)
assert account.balance == 150, "Deposit failed to update balance"
account.withdraw(30)
assert account.balance == 120, "Withdrawal failed to update balance"

try:
    account.withdraw(500)
    assert False, "Should raise ValueError for overdraft"
except ValueError:
    print("✓ Challenge 1 passed!")


# ==========================================
# Challenge 2: Inheritance & Polymorphism
# ==========================================
# Implement a parent class `Employee` and child class `Developer`:
# - `Employee` has: name (str), base_salary (float). Method `calculate_pay()` returns base_salary.
# - `Developer` inherits from `Employee` and adds: programming_language (str).
# - `Developer` overrides `calculate_pay()` to return base_salary + a bonus of 1000.0.

class Employee:
    def __init__(self, name, base_salary):
        # TODO: Set attributes
        self.name = name
        self.base_salary = base_salary

    def calculate_pay(self):
        # TODO: Return base salary
        return self.base_salary

class Developer(Employee):
    def __init__(self, name, base_salary, programming_language):
        # TODO: Call parent constructor and set language
        super().__init__(name, base_salary)
        self.programming_language = programming_language

    def calculate_pay(self):
        # TODO: Return base salary + 1000.0 bonus
        return self.base_salary + 1000.0

# --- Verification ---
emp = Employee("Alice", 5000.0)
dev = Developer("Bob", 6000.0, "Python")

assert emp.calculate_pay() == 5000.0, "Employee pay calculation incorrect"
assert dev.calculate_pay() == 7000.0, "Developer pay calculation incorrect"
assert dev.programming_language == "Python", "Developer language attribute missing"
print("✓ Challenge 2 passed!")


# ==========================================
# Challenge 3: Dunder Methods
# ==========================================
# Create a `Book` class representing a book in a library:
# - Attributes: title (str), author (str), pages (int).
# - Dunder `__str__`: Returns string format "[title] by [author]".
# - Dunder `__len__`: Returns page count.
# - Dunder `__eq__`: Compares two books; returns True if title and author are identical.

class Book:
    def __init__(self, title, author, pages):
        self.title = title
        self.author = author
        self.pages = pages

    # TODO: Implement dunder methods
    def __str__(self):
        return f"{self.title} by {self.author}"

    def __len__(self):
        return self.pages

    def __eq__(self, other):
        if not isinstance(other, Book):
            return False
        return self.title == other.title and self.author == other.author

# --- Verification ---
book1 = Book("Python Basics", "Guido van Rossum", 250)
book2 = Book("Python Basics", "Guido van Rossum", 250)
book3 = Book("Advanced Python", "Raymond Hettinger", 450)

assert str(book1) == "Python Basics by Guido van Rossum", f"Expected 'Python Basics by Guido van Rossum', got '{str(book1)}'"
assert len(book1) == 250, f"Expected page length 250, got {len(book1)}"
assert book1 == book2, "Books with same title and author should be equal"
assert book1 != book3, "Different books should not be equal"
print("✓ Challenge 3 passed!")

print("\n🎉 All tests passed successfully!")